The present invention relates generally to orthotics, and more specifically to a polycentric joint for use in an internal or external knee brace.
The physiological motion of the human knee involves an extremely complex xe2x80x9cpolycentricxe2x80x9d motion wherein the center of rotation of the tibia with respect to the femur varies as a function of the angle of rotation. This motion is caused by the simultaneous movements of the interacting surfaces involved in articulation of the knee, including: (1) rotation of the tibia relative to the femur about a vertical axis; (2) movement between the femoral and tibial parts about a horizontal, anterior-posterior axis; and (3) sliding and anterior-posterior rolling of ends of the femoral and tibial parts in an anterior-posterior plane. The physiological motion of the tibia relative to the femur is further complicated by the three-dimensional component of motion outside the sagittal plane, and by the contribution of ligaments, tendons and cartilage structure.
As a result of contributions from all these factors, a given point on the tibia typically traces a complex, nonlinear curve in the three-dimensional coordinate system of the femur. This curve has been described as a helicoidal motion, which is a description of displacement of the moving bodyxe2x80x94the tibiaxe2x80x94relative to the fixed bodyxe2x80x94the femurxe2x80x94as rotation about, and translation along a screw axis. See A. M. Bull and A. A. Amis, Knee Joint Motion: Description and Measurement, Proc Inst Mech Eng [H] 212 (5):357-72 (1998); H. Jonsson and J. Karrholm, Three-dimensional Knee Joint Movements During a Step-up: Evaluation After Anterior Cruciate Ligament Rupture, J Orthop Res 12(6):769-79 (1994); J. Karrholm et al., Kinematics of Successful Knee Prostheses During Weight-bearing: Three-dimensional Movements and Positions of Screw Axes in the Tricon-M and Miller-Galante Designs, Knee Surg Sports Traumatol Arthrosc 2 (1):50-9 (1994); L. Weidenhielm, Knee Motion After Tibial Osteotomy for Arthrosis. Kinematic Analysis of 7 Patients, Acta Orthop Scand 64 (3):317-19 (1993); R. A. Hart et al., A Finite Helical Axis as a Landmark for Kinematic Reference of the Knee, J Biomech Eng 113 (2):215-22 (1991); L. Blankevoort et al., Helical Axes of Passive Knee Joint Motions, J Biomech 23 (12):1219-29 (1990); R. Shiavi et al., Helical Motion Analysis of the Kneexe2x80x94II. Kinematics of Uninjured and Injured Knees During Walking and Pivoting, J Biomech 20 (7):653-65 (1987); R. Shiavi et al., Helical Motion Analysis of the Kneexe2x80x94I. Methodology for Studying Kinematics During Locomotion, J Biomech 20 (5):459-69 (1987); Y. Kaneda et al., Experimental Study on External Tibial Rotation of the Knee, Am J Sports Med 25 (6):796-800 (1997).
Knee joint endoprosthesis which purportedly replicate the complex polycentric motion of the knee have been proposed. Pappas, U.S. Pat. No. 5,507,820 and Helfet, U.S. Pat. No. 3,748,662, for example, disclose ball and socket knee endoprosthesis in which the ball-like femoral component engages an articulating helicoidal socket-like tibial component to control a complex three-dimensional movement.
Knee support braces which purportedly replicate the complex motion of the knee have also been proposed. Postelmanns, U.S. Pat. No. 5,611,774, for example, discloses a slotted, knee support brace which includes femoral and tibial rods that widen at one end to form corresponding shells. The shells are linked to each other using a pair of guide slots having a predetermined curvature and a pair of studs projecting laterally with respect to the surface of each shell. The femoral and tibial shells also have curved outer surfaces of different predetermined curvature. In the assembled state, the stud of the femoral joint is positioned in the slot of the tibial joint, and vice-versa. The shells are then held together by nuts which are screwed onto the projecting ends of the studs. During flexion, the tibial stud moves near to one end of the slot, following the defined curvature of the slot, and the second stud follows the path defined by the tibial slot. Because the femoral and tibial shells have curved outer surfaces, during flexion, the femoral and tibial shells are not in contact with each other over the whole of their surface. Thus, at all times, the femoral and tibial shells are connected at at least three points, a point determined by the curvatures of the shell surfaces, and two points where the studs interact with the slots.
One disadvantage of the Postelmanns"" knee brace and other traditional knee braces, however, is that they do not readily withstand compression and distraction forces. It has been found that many knee conditions significantly benefit from both polycentric motion as well as compression and distraction of the knee joint. Therefore, there is a need in the art for a knee brace which is capable of controlling a complex polycentric motion but which is also capable of withstanding compression and distraction forces.
The present invention relates to an internal or external knee brace having a polycentric joint that enables control of a predetermined helicoidal motion and which permits compression and distraction of the knee joint. In an apparatus according to the present invention, the knee brace includes a femoral component including a femoral joint member having at least one mating surface with a predetermined contour, and a stem projecting from the femoral joint member for attachment to the upper leg. The knee brace further includes a tibial component including a tibial joint member having at least one bearing surface for contact with the mating surface of the femoral joint member, and a stem projecting from the tibial joint member for attachment to the lower leg. The femoral joint and tibial joint members are in juxtaposition and aligned on opposite sides of a vertical, anterior-posterior plane in a mounting member. At least a portion of the femoral joint member is fixed to the mounting member. The tibial joint member, on the other hand, is rotatable relative to the fixed femoral joint member within the mounting member. The mounting member further includes a resilient member, such as a spring, which is used to bias the tibial joint member toward the femoral joint member.
During rotation of the knee, the bearing surface of the tibial joint member follows the predetermined contour of the mating surface of the femoral joint member resulting in medial or lateral displacement of the tibial component relative to the fixed femoral component as a function of the position of the knee. The displacement is characterized as a helicoidal path during flexion of the knee and a change from a helicoidal path to a straight-line function during extension of the knee.
Although not limited to any particular theory, the ability of the knee brace of the present invention to withstand compression and distraction forces is believed to result from the stability imparted by the arrangement of the joint members in the mounting member. Although the mounting member has a structure which permits the joint member to control a complex polycentric motion, the mounting member also imparts stability to the joint members so as to substantially withstand compression and distraction forces thereby permitting the use of the joint in treating conditions of the knee which can benefit from both polycentric motion as well as compression or distraction of the knee joint.